The purpose of this investigation is to examine the immunogenicity of liposomal model membranes that have been sensitized by the incorporation of phosphatidylethanolamine (PE) deriatives in which the amino group has been substituted with various haptens. These liposomes have determinants (i.e. the N-substituted PE derivatives) inserted non-covalently in lipid bilayers which function as the carrier. They are thus novel immunogens that differ significantly from conventional immunogen preparations in which haptens are covalently attached to carriers such as proteins or amino acid polymers. In spite of this difference, we have already demonstrated that such liposomes can elicit both humoral and cell mediated responses. These observations indicate that liposomes should be used to investigate numerous immunological phenomena that have so far been studied solely with classical hapten-carrier conjugates. Liposomes are uniquely appropriate for this purpose because epitope density, molecular complexity of the determinants, and their chemical environment can be simply regulated by varying the composition of the lipid mixture used to generate the model membranes.